Adobe does not support beta versions of third party software, and Firefox 4 is still in RC status. When it's finally released any compatibility issues will no doubt be addressed within the normal Acrobat and Reader update cycles, but we can't comment on specifics.

There's no information about this on the FF webpage. However, even if it is, then yes, you'll need to wait to the next cycle of updates (or even later) for the FF5 compatability. I guess Mozilla and Adobe are not synchronizing their updates very well...

PS - I don't think that the fact that it appears in the releases folder means much. See the index.html in that folder...